[Date of the letter]
Dear Concerned Person (always refer with first name in case of personal and in case of professional address by surname)

Thank you so much for the lovely gift. I always wanted this gift (elaborate on the gift) and aspired to own it. However, I somehow could never make myself buy it. Thank you once more for being so thoughtful and gifting me such a wonderful gift. Not only is the gift good to look at, but also extremely useful. The gift has in numerous uses like (talk about how you will use the gift) I loved the gift, thanks a lot (elaborate on what you liked).

Thank you for being so caring and thoughtful. Would like you to know that your gift means a lot to me and I will always cherish the same.